Environment Constrains Fitness Advantages of Division of Labor in Microbial Consortia Engineered for Metabolite Push or Pull Interactions

Fitness benefits from division of labor are well documented in microbial consortia, but the dependency of the benefits on environmental context is poorly understood. Two synthetic Escherichia coli consortia were built to test the relationships between exchanged organic acid, local environment, and opportunity costs of different metabolic strategies. Opportunity costs quantify benefits not realized due to selecting one phenotype over another. The consortia catabolized glucose and exchanged either acetic or lactic acid to create producer-consumer food webs. The organic acids had different inhibitory properties and different opportunity costs associated with their positions in central metabolism. The exchanged metabolites modulated different consortial dynamics. The acetic acid-exchanging (AAE) consortium had a “push” interaction motif where acetic acid was secreted faster by the producer than the consumer imported it, while the lactic acid-exchanging (LAE) consortium had a “pull” interaction motif where the consumer imported lactic acid at a comparable rate to its production. The LAE consortium outperformed wild-type (WT) batch cultures under the environmental context of weakly buffered conditions, achieving a 55% increase in biomass titer, a 51% increase in biomass per proton yield, an 86% increase in substrate conversion, and the complete elimination of by-product accumulation all relative to the WT. However, the LAE consortium had the trade-off of a 42% lower specific growth rate. The AAE consortium did not outperform the WT in any considered performance metric. Performance advantages of the LAE consortium were sensitive to environment; increasing the medium buffering capacity negated the performance advantages compared to WT

Science as an Agent of Change: Finalization and Experimental Implementation

Krohn W, van den Daele W. Science as an Agent of Change: Finalization and Experimental Implementation. Social Science Information. 1998;37(1):191-222

The Family Chromatiaceae

The Chromatiaceae is a family of the Chromatiales within the Gammaproteobacteria and closely related to the Ectothiorhodospiraceae. Representatives of both families are referred to as phototrophic purple sulfur bacteria and typically grow under anoxic conditions in the light using sulfide as photosynthetic electron donor, which is oxidized to sulfate via intermediate accumulation of globules of elemental sulfur. In Chromatiaceae species, the sulfur globules appear inside the cells; in Ectothiorhodospiraceae, they are formed outside the cells and appear in the medium. Characteristic properties of these bacteria are the synthesis of photosynthetic pigments, bacteriochlorophyll a or b, and various types of carotenoids and the formation of a photosynthetic apparatus with reaction center and antenna complexes localized within internal membrane systems. Phototrophic growth, photosynthetic pigment synthesis, and formation of the photosynthetic apparatus and internal membranes are strictly regulated by oxygen and light and become derepressed at low oxygen tensions. Typically, Chromatiaceae are enabled to the photolithoautotrophic mode of growth. A number of species also can grow photoheterotrophically using a limited number of simple organic molecules. Some species also can grow under chemotrophic conditions in the dark, either autotrophically or heterotrophically using oxygen as terminal electron acceptor in respiratory processe